Dipolar and quadrupolar correlations in the $5d^2$ Re-based double perovskites Ba$_2$YReO$_6$ and Ba$_2$ScReO$_6$

TL;DR

This study investigates the magnetic and quadrupolar correlations in Re-based double perovskites Ba$_2$YReO$_6$ and Ba$_2$ScReO$_6$ using various experimental techniques, revealing complex magnetic states and excitations.

Contribution

It provides new insights into the dipolar and quadrupolar interactions in heavy transition metal double perovskites, combining experimental data with theoretical modeling.

Findings

Type-I antiferromagnetic ground state observed in both compounds

Identification of a quadrupolar ordered phase above magnetic transitions

Observation of gapped spin excitations and phonon modes

Abstract

Double perovskites containing heavy transition metal ions are an important family of compounds for the study of the interplay between electron correlation and spin-orbit coupling. Here, by combining magnetic susceptibility, heat capacity, and neutron scattering measurements, we investigate the dipolar and quadrupolar correlations in two prototype rhenium-based double perovskite compounds, Ba$_2$YReO$_6$ and Ba$_2$ScReO$_6$. A type-I dipolar antiferromagnetic ground state with a propagation vector $\mathbf{q} = (0, 0, 1)$ is observed in both compounds. At temperatures above the magnetic transitions, a quadrupolar ordered phase is identified. Weak spin excitations, which are gapped at low temperatures and softened in the correlated paramagnetic phase, are explained using a minimal model that considers both the dipolar and quadrupolar interactions. At larger wavevectors, we observe dominant phonon excitations that are well described by density functional calculations.